If someone sleepwalks and then murders/assaults/etc. someone all while they're sleeping, what, if any, responsiblity would they face? Has such a situation ever happened?

Being asleep usually precludes being prosecuted because a sleeping person can't form intent, a necessary component of most crimes.

However there are exceptions - there was, for example, a pretty brutal homicide of a young child in Ireland committed by an Irish Army Ranger (the elite wing of the Irish Defence Forces), while both were sleeping which did result in a manslaughter prosecution.

You mean, the defense has to prove it was done while sleepwalking? Interesting, since usually it is innocent until proven guilty.

Well, but if you admit that you actually killed somebody, you're admitting guilt, simply offering an explanation for it. You wouldn't be contesting the actual cause of death, simply the reason that you caused the death.

You mean, the defense has to prove it was done while sleepwalking? Interesting, since usually it is innocent until proven guilty.

Well, but if you admit that you actually killed somebody, you're admitting guilt, simply offering an explanation for it. You wouldn't be contesting the actual cause of death, simply the reason that you caused the death.

The sleepwalking killer in this case could admit, "I killed this person while I was sleepwalking" and prove with without any admission of guilt. Legally, they wouldn't be admitting guilt to the crime they've been charged with. Because murder requires malice, voluntary manslaughter requires intent, and involuntary manslaughter requires some sort of gross negligence. If none of those factors are present then the killer isn't truly guilty of the crime.

Now, I could possibly see a conviction for involuntary manslaughter (depending on the exact wording of the relevant statute), but only if the prosecution could prove that the defendant already knew about his potentially murderous sleepwalking rampages and was grossly negligent in eliminating the possibility for it to occur. Perhaps that's why the guy was sentenced the second time, but not the first, in J.J.'s example above: he'd already killed while sleepwalking once before so it's pretty damn negligent to not take any sort of precaution to make sure it doesn't happen again.

Well, presumably, the prosecutor would have some reasoning for the intent to kill the person. At which point, it would fall on the defense to counter with the proof that the defendant was sleepwalking.

Point is, for the prosecution to have to prove in each and every case that the defendant was not sleepwalking while allegedly committing the crime would be ridiculous, and the burden of proof would fall on the defense.

Well, presumably, the prosecutor would have some reasoning for the intent to kill the person. At which point, it would fall on the defense to counter with the proof that the defendant was sleepwalking.

Point is, for the prosecution to have to prove in each and every case that the defendant was not sleepwalking while allegedly committing the crime would be ridiculous, and the burden of proof would fall on the defense.

Yes; I was just explaining how/why someone who killed someone while sleepwalking would correctly plead "not guilty" to whatever charges were brought even if they did know they had done it.

And legally, the sleepwalker wouldn't have a burden of proof, per se, the defense would only have the "burden" of casting reasonable doubt over the prosecution's charges (although practically, with something like this, such testimony in favor of sleepwalking would need to be pretty damn convincing).